Buggy code:
public abstract class DefaultAbstractTree extends AbstractTree { private static final long serialVersionUID = 1L ; public static final class LinkType extends EnumeratedType { public static final DefaultAbstractTree . LinkType AJAX = new DefaultAbstractTree . LinkType ( "AJAX" ) ; public static final DefaultAbstractTree . LinkType AJAX_FALLBACK = new DefaultAbstractTree . LinkType ( "AJAX_FALLBACK" ) ; public static final DefaultAbstractTree . LinkType REGULAR = new DefaultAbstractTree . LinkType ( "REGULAR" ) ; private static final long serialVersionUID = 1L ; public LinkType ( String name ) { } } protected interface ILinkCallback extends IClusterable { void onClick ( AjaxRequestTarget target ) { } } private static final ResourceReference CSS = new CompressedResourceReference ( DefaultAbstractTree . class , "res//tree.css" ) ; private static final ResourceReference FOLDER_CLOSED = new PackageResourceReference ( DefaultAbstractTree . class , "res//folder-closed.gif" ) ; private static final ResourceReference FOLDER_OPEN = new PackageResourceReference ( DefaultAbstractTree . class , "res//folder-open.gif" ) ; private static final ResourceReference ITEM = new PackageResourceReference ( DefaultAbstractTree . class , "res//item.gif" ) ; private DefaultAbstractTree . LinkType linkType = DefaultAbstractTree . LinkType . AJAX ; public DefaultAbstractTree ( String id ) { } public DefaultAbstractTree ( String id , IModel < TreeModel > model ) { } public DefaultAbstractTree ( String id , TreeModel model ) { } public DefaultAbstractTree . LinkType getLinkType ( ) { } public void setLinkType ( DefaultAbstractTree . LinkType linkType ) { } protected ResourceReference getCSS ( ) { } protected ResourceReference getFolderClosed ( ) { } protected ResourceReference getFolderOpen ( ) { } protected ResourceReference getItem ( ) { } protected ResourceReference getNodeIcon ( TreeNode node ) { } protected Component newIndentation ( MarkupContainer parent , String id , final TreeNode node , final int level ) { } protected MarkupContainer newJunctionImage ( MarkupContainer parent , final String id , final TreeNode node ) { } protected Component newJunctionLink ( MarkupContainer parent , final String id , final String imageId , final TreeNode node ) { } protected MarkupContainer newLink ( MarkupContainer parent , String id , final DefaultAbstractTree . ILinkCallback callback ) { } protected Component newNodeIcon ( MarkupContainer parent , String id , final TreeNode node ) { return new WebMarkupContainer ( id ) { private static final long serialVersionUID = 1L ; @ Override protected void onComponentTag ( ComponentTag tag ) { super . onComponentTag ( tag ) ; IRequestHandler handler = new org . apache . wicket . request . handler . resource . ResourceReferenceRequestHandler ( getNodeIcon ( node ) ) ; <START_BUG> tag . put ( "style" , ( ( "background-image:<seq2seq4repair_space>url('" + ( RequestCycle . get ( ) . renderUrlFor ( handler ) ) ) + "')" ) ) ; <END_BUG> } } ; } protected MarkupContainer newNodeLink ( MarkupContainer parent , String id , final TreeNode node ) { } protected void onJunctionLinkClicked ( AjaxRequestTarget target , TreeNode node ) { } protected void onNodeLinkClicked ( AjaxRequestTarget target , TreeNode node ) { } private boolean isNodeLast ( TreeNode node ) { } @ Override public void renderHead ( IHeaderResponse response ) { } }

Fix:
tag . put ( "style" , ( ( "background-image:<seq2seq4repair_space>url('" + ( RequestCycle . get ( ) . urlFor ( handler ) ) ) + "')" ) ) ;